A ventilator delivers a flow of pressurized gas, such as air and/or a mixture of air and extra (supplemental) oxygen, to the airway of a patient in order to assist in or substitute for the patient's breathing. A ventilator operates cyclically, such that the gas is provided to the patient during an inspiratory phase (corresponding to inhalation) and received from the patient during a subsequent expiratory phase (corresponding to exhalation). In order to provide a mixture of air and extra oxygen, for example, the ventilator receives air through an air pathway and pure oxygen through a separate oxygen pathway, and thus controls respective levels of each gas to obtain the desired mixture, provided to the patient during the inspiratory phase.
Generally, the patient interacts with a ventilator through conduits or “limbs,” which conduct gas flow. A single limb ventilator provides a single conduit for inspiratory and expiratory phases, meaning that the patient receives (pressurized) gas from the ventilator during inhalation and discharges gas to the ventilator during exhalation through the same conduit. Typically, the discharged gas is directed through the air pathway of the ventilator. When the inspiratory gas flow includes a mixture of air and oxygen, for example, the expiratory gas flow necessarily includes at least a portion of the extra oxygen, resulting in “oxygen contamination” in the air pathway. Therefore, during the subsequent cycle of the inspiratory gas flow, the gas from the air pathway includes a higher concentration of oxygen than pure air. When the gas from the air pathway is mixed with additional oxygen from the oxygen pathway, the mixed gas provided to the patient has a higher than desired concentration of oxygen.
In order to ensure that the proper mixture of air and oxygen are provided, a sample of the mixture is taken. Because of limitations of known flow meters used in the determination of the mixture, the flow rate or flow volume of the sample is generally much smaller than that of the ventilator. Presenting the sample can be problematic, particularly in view of the limitations of the flow sensors and volume sensors. Moreover, sensing the oxygen and air in both inspiration and expiration can cause obstructions and compromised flow.
In one aspect, a ventilator includes a first pathway configured to supply a first gas; a second pathway configured to supply a second gas; a bypass element configured to provide a portion of the first gas and a portion of the second gas, the bypass element comprising a rib adjacent to a bypass conduit, wherein fluid flow is substantially laminar adjacent to the conduit.
In another aspect, a bypass element configured to direct a first gas and a second gas from a ventilator, the bypass element comprising: a rib adjacent to a bypass conduit, wherein fluid flow is substantially laminar adjacent to the conduit.